Method of manufacturing S-glass fibers in a direct melt operation and products formed there from

ABSTRACT

A method of forming high strength glass fibers in a refractory-lined glass meter, products made there from and batch compositions suited for use in the method are disclosed. The glass composition for use in the method of the present invention is up to about 64-75 weight percent SiO 2 , 16-24 weight percent Al 2 O 3 , 8-12 weight percent MgO and 0.25-3 weight percent R 2 O, where R 2 O equals the sum of Li 2 O and Na 2 O, has a fiberizing temperature less than about 2650° F., and a ΔT of at least 80° F. By using oxide-based refractory-lined furnaces the cost of production of glass fibers is substantially reduced in comparison with the cost of fibers produced using a platinum-lined melting furnace. High strength composite articles including the high strength glass fibers are also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-Part of U.S. patent application Ser. No. 12/341,985 entitled “Composition for High Performance Glass Fibers and Fibers Formed Therewith” filed Dec. 22, 2008, the entire content of which is expressly incorporated herein by reference. This application is also a Continuation-in-Part of U.S. patent application Ser. No. 11/267,702 entitled “Method of Manufacturing High Performance Glass Fibers in a Refractory Lined Melter and Fibers Formed Thereby” filed Nov. 4, 2005, the entire content of which is also expressly incorporated herein by reference. This application is also a Continuation-in-Part of U.S. patent application Ser. No. 11/267,739 entitled “Composition for High Performance Glass, High Performance Glass Fibers and Articles Therefrom” filed Nov. 4, 2005, the entire content of which is also expressly incorporated herein by reference.

TECHNICAL FIELD AND INDUSTRIAL Applicability of the Invention

The present invention is generally directed to a method of manufacturing continuous glass fibers for use in high-strength applications and products made there from, such as ballistic armor, pressure vessels, structural aerospace materials, structural marine materials, and structural materials for wind energy such as windmill masts and blades.

BACKGROUND OF THE INVENTION

Fiberglass reinforced composite materials have been available for use in marine and aerospace materials for some time. Other fiber materials such as carbon and aramid fibers are available for use, although at substantially higher cost. The articles of the present invention may use any known manufacturing method, including compression molding, laminating, spray up, hand laying, prefabricated lay-up (prepreg), compression molding, vacuum bag molding, pressure bag molding, press molding, transfer molding, vacuum assisted resin transfer molding, pultrusion molding, filament winding, casting, autoclave molding, centrifugal casting resin transfer and continuous casting. The properties of the composite are controlled by the fibers and the resin, and synergy between the two, that produces material properties unavailable from the individual materials.

A number of resins are useful in the manufacture of composite articles including polyester resin, vinylester resin and epoxy resin. Polyester resin is suitable for a number of situations. Vinylester resin has lower viscosity pressure and more flexible postcure than polyester resin and is typically more resistant to degradation. Epoxy resin is typically transparent when cured. Epoxy resin is a polyether resin formed by the polymerization bisphenol A, bisphenol F, bisphenol C, and compounds of similar structure with epichlorohydrin resulting in the formation of the reactive oxirane linkage. Epoxy resins may react with a variety of curing agents, including amines, anhydrides, mercaptans, polyesters to form an infusable solid. The reaction is a condensation reaction typically does not create by-products. Cured epoxy resins have high strength, and low shrinkage during curing. They are used as coatings, adhesives, castings, composites, or foam. Epoxy resins are also desirable for use in high strength applications as a structural matrix material or as a structural glue. Phenolics are thermosetting resins formed by the condensation of phenol, or of a phenol derivative, with an aldehyde, typically a formaldehyde. Phenolics are used chiefly in the manufacture of paints and plastics. Other specific high strength modulus resins include bismaleimide, poly-amide, vinyl ester phenolic, ethylene-acrylate or methacrylate copolymers, high strength medium modulus thermoplastics such as an ionomer (i.e. crosslinked ethylene-methyl acrylate or methyl methacrylate copolymer), polycarbonate, polyurethane, nylon, aramid, modified epoxies.

The most common high strength glass composition for making continuous glass fiber strands is “S-Glass.” S-Glass is a family of glasses composed primarily of the oxides of magnesium, aluminum, and silicon with a chemical composition that produces glass fibers having a higher mechanical strength than E-Glass fibers. A commonly used member of the S-Glass family is known as S2-Glass. S2-Glass includes approximately 65 weight % SiO₂, 25 weight % Al₂O₃, and 10 weight % MgO. S-glass has a composition that was originally designed to be used in high-strength applications such as ballistic armor.

R-Glass is a family of glasses that are composed primarily of the oxides of silicon, aluminum, magnesium, and calcium with a chemical composition that produces glass fibers with a higher mechanical strength than E-Glass fibers. R-Glass has a composition that contains approximately 58-60 weight % SiO₂, 23.5-25.5 weight % Al₂O₃, 14-17 weight % CaO plus MgO, 0% B₂O₃, 0% F₂ and less than 2 weight % miscellaneous components. R-Glass contains more alumina and silica than E-Glass and requires higher melting and processing temperatures during fiber forming. Typically, the melting and processing temperatures for R-Glass are at least 160° C. higher than those for E-Glass. This increase in processing temperature typically requires the use of a high-cost platinum-lined melter. In addition, the close proximity of the liquidus temperature to the forming temperature in R-Glass requires that the glass be fiberized at a higher temperature than E-Glass.

Tables IA-IE set forth the compositions for a number of conventional high-strength glass compositions.

TABLE I-A Chinese RUSSIAN High CONTINUOUS NITTOBO “T” Strength ROVING MAGNESIUM NITTOBO “T” Glass Fabric Constituent glass ALUMINOSILICATE Glass Fabric “B” (Yarn) “C” SiO₂ 55.08 55.81 64.58 64.64 CaO 0.33 0.38 0.44 0.40 Al₂O₃ 25.22 23.78 24.44 24.57 B₂O₃ 1.85 0.03 0.03 MgO 15.96 15.08 9.95 9.92 Na₂O 0.12 0.063 0.08 0.09 Fluorine 0.03 0.034 0.037 TiO₂ 0.023 2.33 0.019 0.018 Fe₂O₃ 1.1 0.388 0.187 0.180 K₂O 0.039 0.56 0.007 0.010 ZrO₂ 0.007 0.15 Cr₂O₃ 0.011 0.003 0.003 Li₂O 1.63 CeO₂

TABLE I-B Nitto Nitto Vetrotex Saint Boseki Boseki Nitto Boseki TE Gobain SR Glass Polotsk A&P NT6030 Glass RST- Stratifils SR CG STEKLOVOLOKNO Constituent Yarn Yarn 220PA-535CS 250 P109 High Strength Glass SiO₂ 65.51 64.60 64.20 63.90 58.64 CaO 0.44 0.58 0.63 0.26 0.61 Al₂O₃ 24.06 24.60 25.10 24.40 25.41 B₂O₃ 0.04 MgO 9.73 9.90 9.90 10.00 14.18 Na₂O 0.04 0.06 0.020 0.039 0.05 Fluorine 0.07 0.02 TiO₂ 0.016 0.000 0.000 0.210 0.624 Fe₂O₃ 0.067 0.079 0.083 0.520 0.253 K₂O 0.020 0.020 0.020 0.540 0.35 ZrO₂ 0.079 Cr₂O₃ 0.0010 0.001 0.023 Li₂O CeO₂

TABLE I-C Chinese High Chinese High Strength Yarn Strength Glass Zentron S-2 SOLAIS Glass Advanced Glass Constituent (8 micron) Roving Glass Roving Sample Yarns R Glass SiO₂ 55.22 55.49 64.74 64.81 58.46 CaO 0.73 0.29 0.14 0.55 9.39 Al₂O₃ 24.42 24.88 24.70 24.51 24.55 B₂O₃ 3.46 3.52 0.02 0.04 MgO 12.46 12.28 10.24 9.35 5.91 Na₂O 0.104 0.06 0.17 0.16 0.079 Fluorine 0.07 0.02 0.054 TiO₂ 0.32 0.36 0.015 0.04 0.196 Fe₂O₃ 0.980 0.930 0.045 0.238 0.400 K₂O 0.240 0.150 0.005 0.03 0.67 ZrO₂ Cr₂O₃ 0.0050 0.007 0.005 Li₂O 0.59 0.63 CeO₂ 1.23 1.25

TABLE I-D Advanced IVG Vertex Glass Yarns Culimeta IVG Vertex B96 IVG Vertex Outside #1 Glass Constituent S Glass Roving 675 Yarn Glass Roving Roving SiO₂ 64.61 59.37 58.34 58.58 58.12 CaO 0.17 0.27 0.31 0.30 0.31 Al₂O₃ 24.84 25.49 23.81 24.26 24.09 B₂O₃ 0.04 0.05 MgO 10.11 13.47 14.99 15.02 15.36 Na₂O 0.118 0.024 0.05 0.02 0.03 Fluorine 0.03 0.04 0.04 0.04 TiO₂ 0.011 0.530 1.380 0.67 0.91 Fe₂O₃ 0.042 0.374 0.333 0.336 0.303 K₂O 0.48 0.42 0.28 0.29 ZrO₂ 0.152 0.129 0.165 0.157 Cr₂O₃ 0.0050 0.0120 0.0100 0.0120 0.0120 Li₂O CeO₂

TABLE I-E IVG Vertex RH CG250 Outside #2 P109 Glass Constituent Glass Roving Fiber Strand SiO₂ 58.69 58.54 CaO 0.29 9.35 Al₂O₃ 24.3 25.39 B₂O₃ MgO 15.06 6.15 Na₂O 0.03 0.10 Fluorine 0.04 0.16 TiO₂ 0.64 0.008 Fe₂O₃ 0.331 0.069 K₂O 0.36 0.14 ZrO₂ 0.187 0.006 Cr₂O₃ 0.0130 Li₂O CeO₂

Both R-Glass and S-Glass are produced by melting the constituents of the compositions in a platinum-lined melting container. The costs of forming R-Glass and S-Glass fibers are dramatically higher than E-Glass fibers due to the cost of producing the fibers in such melters. Thus, there is a need in the art for methods of forming glass compositions useful in the formation of high performance glass fibers from a direct-melt process in a refractory-lined furnace and products formed there from.

SUMMARY OF THE INVENTION

The invention, in part, is a method of manufacturing a glass composition for the formation of continuous glass fibers that are suitable for use in high-strength applications. The composition useful in the present invention may be inexpensively formed into glass fibers using low-cost, direct melting in refractory-lined furnaces due to the relatively low fiberizing temperature of the glass fibers. One composition useful in the present invention includes 64-75 weight % SiO₂, 16-24 weight % Al₂O₃, 8-12 weight % MgO and 0.25 to 3.0 weight % R₂O where R₂O is the sum of Li₂O and Na₂O. In certain embodiments, the glass composition is composed of 64-70 weight % SiO₂, 17-22 weight % Al₂O₃, 9-12 weight % MgO and 1.75-3.0 weight % R₂O where R₂O is the sum of Li₂O and Na₂O. In another embodiment, a glass composition useful in the present invention is composed of 64-70 weight % SiO₂, 17-22 weight % Al₂O₃, 9-12 weight % MgO and 1.75-3.0 weight % Li₂O. In certain embodiments, the composition does not contain more than about 5.0 weight % of compounds such as CaO, P₂O₅, ZnO, ZrO₂, SrO, BaO, SO₃, F₂, B₂O₃, TiO₂ and Fe₂O₃.

The composition preferably does not contain more than about 4 weight % of compounds or halogens such as ZnO, SO₃, Fluorine, B₂O₃, TiO₂, ZrO₂ and Fe₂O₃. The desired properties of the high performance composite fibers manufactured by the present invention include a fiberizing temperature of less than 2650° F. and a liquidus temperature that is preferably below the fiberizing temperature by at least 80° F., more preferably by at least about 120° F., and most preferably by at least about 150° F.

The present invention includes a process for producing refined glass from a raw glass batch in a refractory-lined glass melter. The process includes charging a raw glass batch to a melting zone of a glass melter, melting the raw glass batch within the melting zone and forming fibers from the melt. The present invention also includes fibers formed by such a method, and products made from such fibers.

The present invention also provides a structural part having improved structural properties with decreased costs and improved manufacturability. The direct melt formation of the continuous glass fibers uses low-cost melting in refractory-lined furnaces. The relatively low fiberizing temperature of the glass fibers used in the high-strength applications of the present invention allows improved fiber processing at decreased cost. The articles of the present invention are typically formed by compression molding, laminating, spray up, hand laying, prefabricated lay-up (prepreg), compression molding, vacuum bag molding, pressure bag molding, press molding, transfer molding, vacuum assisted resin transfer molding, pultrusion molding, filament winding, casting, autoclave molding, centrifugal casting resin transfer or continuous casting. The fibers used in the present invention are substantially less expensive to make and also have good strength and density properties. The density of the fibers used in the present invention range between 2.434-2.486 glee and have a measured modulus of 12.71-12.96 MPsi and a measured strength of 688-737 KPsi.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional longitudinal view of a glass melting furnace useful with the method of the present invention;

FIG. 2 is a cross-sectional plan view of the glass melting furnace of FIG. 1 taken along line 2-2;

FIG. 3 is a cross-sectional view of the glass melting furnace of FIG. 1 taken along line 3-3 illustrating two burners adjacent the upstream end wall of the furnace;

FIG. 4 is an alternate cross-sectional plan view of the glass melting furnace of FIG. 1 taken along line 3-3 illustrating one burner adjacent the upstream end wall of the furnace; and

FIG. 5 is a side view, partially in cross section, of a bushing assembly/support structure arrangement for producing continuous glass filaments useful in the method of the present invention.

DETAILED DESCRIPTION AND PREFERRED Embodiments of the Invention

Fiberizing properties of the glass composition used to form the glass fibers of the present invention include the fiberizing temperature, the liquidus, and delta-T. The fiberizing temperature is defined as the temperature that corresponds to a viscosity of 1000 Poise. As discussed in more detail below, a lowered fiberizing temperature reduces the production cost of the fibers, allows for a longer bushing life, increases throughput, permits the glass to be melted in a refractory-lined melter, and reduces energy usage. For example, at a lower fiberizing temperature, a bushing operates at a cooler temperature and does not “sag” as quickly. Sag is a phenomenon that occurs in bushings that are held at an elevated temperature for extended periods of time. By lowering the fiberizing temperature, the sag rate of the bushing may be reduced and the bushing life can be increased. In addition, a lower fiberizing temperature allows for a higher throughput since more glass can be melted in a given period at a given energy input. As a result, production cost is reduced. In addition, a lower fiberizing temperature will also permit glass formed with the inventive method and composition to be melted in a refractory-lined melter since both its melting and fiberizing temperatures are below the upper use temperatures of many commercially available refractories.

The liquidus is defined as the highest temperature at which equilibrium exists between liquid glass and its primary crystalline phase. At all temperatures above the liquidus, the glass is free from crystals in its primary phase. At temperatures below the liquidus, crystals may form.

Another fiberizing property is delta-T (ΔT), which is defined as the difference between the fiberizing temperature and the liquidus. A larger ΔT offers a greater degree of flexibility during the formation of the glass fibers and helps to inhibit devitrification of the glass (that is, the formation of crystals within the melt) during melting and fiberizing. Increasing the ΔT also reduces the production cost of the glass fibers by allowing for a greater bushing life and by providing a wider process window for forming fibers.

The glass compositions employed in the present invention are advantageously suitable for melting in traditional, commercially available refractory-lined glass melters. Starting batch components typically include SiO₂ (ground silica sand), and Al₂O₃ (calcined alumina), Li₂CO₃ (lithium carbonate), H₃BO₃ (boric acid), NaCaB₅O₉.8H₂O (ulexite), 2CaO-3B₂O₃-5h₂O (colmanite) as well as chain modifiers from source materials such as MgCO₃ (magnesite), CaCO₃ (limestone), SrCO₃ (strontianite), BaCO₃ (witherite), ZrSiO₄ (zircon), and Na₂CO₃ (natrite).

FIGS. 1-4 depict a glass melting furnace 10 useful in the method of forming the glass fibers described herein and set forth in the examples and claims below. It may also be desirable to use oxygen-fired heating within the melting furnace, as disclosed in U.S. patent application Ser. No. 10/116,432 entitled “OXYGEN-FIRED FRONT END FOR GLASS FORMING OPERATION”, inventors David J Baker et al., and published as U.S. Published Application No. 2003/0188554, herein incorporated in its entirety by reference. The glass melting furnace 10 provides molten glass to a glass forehearth 12. The molten glass is preferably composed of about 64-75 weight % SiO₂, 16-24 weight % Al₂O₃, 8-12 weight % MgO and 0.25 to 3.0 weight % R₂O where R₂O is the sum of Li₂O and Na₂O. In certain embodiments, the composition does not contain more than about 5.0 weight % of oxides or compounds such as CaO, P₂O₅, ZnO, ZrO₂, SrO, BaO, SO₃, F₂, B₂O₃, TiO₂ and Fe₂O₃.

In addition, a fiber formed in accordance with the method and composition of the present invention will have a fiberizing temperature of less than 2650° F., and in certain embodiments less than about 2625° F., in other embodiments less than about 2600° F. and in certain embodiments less than about 2575° F. and a liquidus temperature that is below the fiberizing temperature in certain embodiments by at least 80° F., and in other embodiments by at least about 120° F., and in yet other embodiments by at least about 150° F. Further, the glass fibers of the present invention, in certain embodiments, will have a pristine fiber strength in excess of 680 KPSI, and in certain other embodiments a strength in excess of about 700 KPSI, and in yet other embodiments a strength in excess of about 730 KPSI. Further, the glass fibers will advantageously have a modulus greater than 12.0 MPSI, and in certain embodiments greater than about 12.18 MPSI, and in some embodiments greater than about 12.6 MPSI.

The method of the present invention is preferably performed using the glass melting furnace 10, which includes an elongated channel having an upstream end wall 14, a downstream end wall 16, side walls 18, a floor 20, and a roof 22. Each of the components of the glass melting furnace 10 are made from appropriate refractory materials such as alumina, chromic oxide, silica, alumina-silica, zircon, zirconia-alumina-silica, or similar oxide-based refractory materials. The roof 22 is shown generally as having an arcuate shape transverse to the longitudinal axis of the composition the channel; however, the roof may have any suitable design. The roof 22 is typically positioned between about 3-10 feet above the surface of the glass batch composition 30. The glass batch material 30 is a mixture of raw materials used in the manufacture of glass in the accordance with the present invention. The glass melting furnace 10 may optionally include one more bubblers 24 and/or electrical boost electrodes (not shown). The bubblers 24 and/or electrical boost electrodes increase the temperature of the bulk glass and increase the molten glass circulation under the batch cover.

In addition, the glass melting furnace 10 may include two successive zones, an upstream melting zone 26 and a downstream refining zone 28. In the melting zone 26, the glass batch composition 30 may be charged into the furnace using a charging device 32 of a type well-known in the art.

In one suitable melter configuration, the glass batch material 30 forms a batch layer of solid particles on the surface of the molten glass in the melting zone 26 of the glass melting furnace 10. The floating solid batch particles of the glass batch composition 30 are at least partially melted by at least one burner 34 having a controlled flame shape and length mounted within the roof 22 of the glass melting furnace 10.

In one preferred embodiment, as shown in FIG. 1, the glass melting furnace 10 includes three burners 34. A single burner 34 is positioned upstream of two adjacently positioned downstream burners 34. However, it will be appreciated that any number of burners 34 may be positioned at any suitable location in the roof 22 of the furnace 10 over the batch to melt the glass batch composition 30. For example, two burners 34 may be positioned in a side-by-side relationship (FIG. 3) or a single burner may be used (FIG. 4).

Other conventional melters may be used without departing from the present invention. Conventional melters include Air-Gas melters, Oxygen-Gas melters, electrically fired melters, or any fossil fuel fired melter. It is possible to add electric boost or bubblers to any of the melting processes. It is also possible to include a separate refining zone (as shown in FIG. 1) or incorporate the refining zone into the main tank of the melter.

As shown in FIG. 5, a bushing assembly 100 includes a bushing 110 and a bushing frame 210. The bushing 110 includes a bushing main body 120 with sidewalls 122 and a tip plate 124 extending between the sidewalls 122. The main body 120 is positioned below a bushing block 300 that, in turn, is positioned beneath a forehearth 310. In practicing the method of the present invention, a stream of molten glass is received by the main body 120 from the forehearth 310. The forehearth 310 receives the molten glass from a melter 10 (shown in FIG. 1). A delivery channel 40 is positioned between the melter 10 and the forehearth 310 to deliver the molten glass batch composition 30 from the melter 10 to the forehearth 310. The forehearth 310 and bushing block 300 may be conventional in construction and may be formed from refractory materials.

The tip plate 124 contains a plurality of nozzles 124 a (also referred to as orifices) through which a plurality of streams of molten glass may be discharged. The streams of molten material may be mechanically drawn from the tip plate 124 to form continuous filaments 125 via a conventional winder device 400. The filaments 125 may be gathered into a single continuous strand 125 a after having received a protective coating of a sizing composition from a sizing applicator 410. The continuous filaments 125 a may be wound onto a rotating collet 402 of the winder device 400 to form a package 125 b. The continuous filaments 125 may also be processed into other desired composite glass materials including, without limitation, wet use chopped strand fibers, dry use chopped strand fibers, continuous filament mats, chopped strand mats, wet formed mats or air laid mats.

High strength articles of the present invention use the formed fibers described above as glass fiber reinforcement within a polymer matrix material. Typical matrix materials include epoxies, phenolic resins, vinylesters, and polyesters. The articles may be formed by any suitable manufacturing technique including compression molding, laminating, spray up, hand laying, prefabricated lay-up (prepreg), compression molding, vacuum bag molding, pressure bag molding, press molding, transfer molding, vacuum assisted resin transfer molding, pultrusion molding, filament winding, casting, autoclave molding, centrifugal casting resin transfer and continuous casting.

Having generally described this invention, a further understanding can be obtained by reference to certain specific examples illustrated below which are provided for purposes of illustration only and are not intended to be all inclusive or limiting unless otherwise specified.

EXAMPLES

The glasses in the examples listed in Tables IIA-IIC were melted in platinum crucibles or in a continuous platinum-lined melter for determining the mechanical and physical properties of the glass and fibers produced there from. The units of measurement for the physical properties are: Viscosity (° F.), Liquidus temperature (° F.) and ΔT (° F.). In some examples the glasses were fiberized and Strength (KPsi), Density (g/cc), and Modulus (MPsi) were measured.

The fiberizing temperature was measured using a rotating spindle viscometer. The fiberizing viscosity is defined as 1000 Poise. The liquidus was measured by placing a platinum container filled with glass in a thermal gradient furnace for 16 hours. The greatest temperature at which crystals were present was considered the liquidus temperature. The modulus was measured using the sonic technique on a single fiber of glass. The tensile strength was measured on a pristine single fiber.

TABLE II-A Glass Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 SiO₂ 67.2 69 67 70 70 65 Al₂O₃ 20 22 22 17 17 21 MgO 9.8 9 11 11 10 11 Li₂O 3 0 0 2 3 3 Measured 2531 2761 2648 2557 2558 2461 Viscosity (° F.) 1^(st) Measured 2313 2619 2597 2332 2302 2296 Liquidus (° F.) 2^(nd) Measured 2302 2620 2614 2346 2308 2318 Liquidus (° F.) ΔT (° F.) 218 142 51 225 256 165 Measured 2.459 2.452 2.481 2.450 2.441 2.482 Density (g/cc)

TABLE II-B Glass Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 SiO₂ 70 69 70 65 66 65 Al₂O₃ 18 17 21 22 22 22 MgO 9 11 9 11 9 10 Li₂O 3 3 0 2 3 3 Measured 2544 2496 2752 2525 2523 2486 Viscosity (° F.) 1^(st) Measured 2311 2234 2597 2468 2391 2361 Liquidus (° F.) 2^(nd) Measured 2324 2343 2603 2462 2394 2382 Liquidus (° F.) ΔT (° F.) 233 262 155 57 132 125 Measured 2.434 2.455 2.443 2.486 2.460 2.474 Density (g/cc)

TABLE II-C Glass Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18 SiO₂ 70 67.32 67.57 68.27 68.02 67.76 Al₂O₃ 19 20.49 20.49 20.10 20.10 20.10 MgO 11 10.00 10.00 9.69 9.69 9.69 Li₂O 0 2.00 1.75 1.75 2.00 2.25 Measured 2679 2563 2584 2598 2578 2547 Viscosity (° F.) 1^(st) Measured 2596 2456 2486 2446 2431 2399 Liquidus (° F.) 2^(nd) Measured 2582 2447 2469 2469 2437 2406 Liquidus (° F.) ΔT (° F.) 83 111.5 106.5 140.5 144 144.5 Measured 2.453 2.461 2.452 Density (g/cc)

The composition of the present invention may also include chain modifiers such as Na₂O, CaO and B₂O₃. Such compositions are shown in Table II-D (below).

TABLE II-D Glass Ex. 19 Ex. 21 Ex. 22 Ex. 22 Ex. 23 Ex. 24 SiO₂ 75 66 65 65 66 74 Al₂O₃ 15 20 20 24 19 15 MgO 8 9 8 8 9 8 Li₂O 1 1 2 0 0 0 Na₂O 1 2 1 1 2 3 CaO 2 4 B₂O₃ 2 4 Measured 2765 2607 2469 2669 2809 Viscosity (° F.) 1^(st) Measured 2422 2729 2614 2630 2680 Liquidus (° F.) ΔT (° F.) 343 −122 55 129

The fibers of the present invention have superior modulus and strength characteristics. The fibers of Example 1 have a Measured Modulus of 12.71 MPsi and a Measured Strength of 688 KPsi. The fibers of Example 3 have a Measured Modulus of 12.96 MPsi and a Measured Strength of 737 KPsi. The fibers of Example 17 have a Measured Modulus of 12.75 MPsi and a Measured Strength of 734 KPsi.

As is understood in the art, the above exemplary inventive compositions do not always total 100% of the listed components due to statistical conventions (such as, rounding and averaging) and the fact that some compositions may include impurities that are not listed. Of course, the actual amounts of all components, including any impurities, in a composition always total 100%. Furthermore, it should be understood that where small quantities of components are specified in the compositions, for example, quantities on the order of about 0.05 weight percent or less, those components may be present in the form of trace impurities present in the raw materials, rather than intentionally added.

Additionally, components may be added to the batch composition, for example, to facilitate processing, that are later eliminated, thereby forming a glass composition that is essentially free of such components. Thus, for instance, minute quantities of components such as fluorine and sulfate may be present as trace impurities in the raw materials providing the silica, lithia, alumina, and magnesia components in commercial practice of the invention or they may be processing aids that are essentially removed during manufacture.

As is apparent from the above examples, glass fiber compositions of the invention have advantageous properties, such as low fiberizing temperatures and wide differences between the liquidus temperatures and the fiberizing temperatures (high ΔT values). Other advantages and obvious modifications of the invention will be apparent to the artisan from the above description and further through practice of the invention). The high-performance glass of the present invention melts and refines at relatively low temperatures, has a workable viscosity over a wide range of relatively low temperatures, and a low liquidus temperature range.

The invention of this application has been described above both generically and with regard to specific embodiments. Although the invention has been set forth in what is believed to be the preferred embodiments, a wide variety of alternatives known to those of skill in the art can be selected within the generic disclosure. Other advantages and obvious modifications of the invention will be apparent to the artisan from the above description and further through practice of the invention. The invention is not otherwise limited, except for the recitation of the claims set forth below. 

We claim:
 1. A process for producing glass from raw glass-forming material in a refractory-lined glass melter, the glass melter having a roof, a bottom and side walls, defining an elongated channel having a melting zone and a downstream refining zone, the process comprising the steps of: charging raw glass batch to the melting zone of the refractory-lined glass melter, the glass batch comprising: 68-69 weight percent SiO₂; 20-22 weight percent Al₂O₃; 9-10 weight percent MgO; no more than 2.0 weight percent CaO; and 1-3 weight percent Li₂O; providing at least one burner within the roof of the glass melter; and melting the glass batch to form a fiberizable molten glass, wherein said molten glass produced has a fiberizing temperature of less than about 2650° F.
 2. The process of claim 1, wherein said glass fibers produced have a strength of greater than about 700 KPsi.
 3. The process of claim 1, wherein the glass batch comprises: less than 5 weight percent total of compounds selected from the group consisting of P₂O₃, ZnO, ZrO₂, SrO, BaO, SO₃, F2, B₂O₃, TiO₂ and Fe₂O₃.
 4. The process of claim 1, wherein glass produced from the batch is fiberized at a foiniing temperature of less than 2600° F.
 5. The process of claim 1, wherein said molten glass produced from the batch has a liquidus temperature, wherein the difference (ΔT) between the fiberizing temperature and the liquidus temperature is 140° F.
 6. A process for producing glass fibers from raw glass batch in a refractory-lined glass melter, the process comprising the steps of: charging raw glass batch to the melting zone of a refractory-lined glass melter, the glass batch comprising: about 68-69 weight percent SiO₂; about 20-22 weight percent Al₂O₃; about 9-10 weight percent MgO; no more than 2.0 weight percent CaO; and about 1-3 weight percent Li₂O, heating the glass batch to form a fiberizable molten glass having a fiberizing temperature of less than about 2650° F.; and fiberizing said molten glass to produce glass fibers having a strength of greater than about 700 KPsi. 